Method of making an electromagnetic device

ABSTRACT

A bifurcated magnetic core in an electromagnetic device having an armature plate is formed with a fixedly mounted yoke and pair of arms which cooperate with the armature plate and are each provided with a pole surface facing the same. The inherent frequency of the fundamental oscillation of the magnet core prior to application of a winding onto the same is in excess of 25 kilohertz.

United States Patent 1 Riimer et a].

[ June 19, 1973 METHOD OF MAKING AN ELECTROMAGNETIC DEVICE Inventors:Kurt Riimer, Altbach/Neckar; Josef Schmid; Adolf Krajc, both ofWernau/Neckar, all of Germany Assignee: Junkers & Co. Gmbll, I

Wernau/Neckan, Germany Filed: Aug. 20, 1971 Appl. No.: 173,592

Related US. Application Data Division of Ser. No. 883,004, Dec. 8,abandoned.

Foreig p Application Priority Data July 5, 1969 Germany P 19 34 163.0

Int. CL. H02k 15/00, H02k 15/14, H02k 15/16 Field of Search 29/602, 607,596;

[56] References Cited UNITED STATES PATENTS 3,156,836 11/1964 Koke310/29 3,039,012 6/1962 Bruninghaus 310/29 Primary ExaminerCharles W.Lanham Assistant Examiner-Carl E. Hall Attorney-Michael S. Striker [57]ABSTRACT 7 Claims, 4 Drawing Figures pmmmq'um sun War 1 w.

METHOD OF MAKING AN ELECTROMAGNETIC DEVICE CROSS REFERENCE TO RELATEDAPPLICATION This is a division of our copending application Ser. No.883,004, now abandoned filed on Dec. 8, 1969.

BACKGROUND OF THE INVENTION The present invention relates generally toelectromagnetic devices, and more particularly to a method of making anelectromagnetic device.

It is known to provide thermoelectric ignition safety devices in certainappliances, particularly in appliances using combustible gas. Suchdevices comprise an anchor plate cooperating with a plunger and beingassociated with the free ends of two arms of a bifurcated magnet corewhose yoke is fixedly mounted and which carries the magnet winding.There are applications wherein this type of construction is entirelysatisfactory. In other applications, however, it has been found thatthese devices require improvement. The holding power of theelectromagnet and the closure time of the ignition safety device whichis operated by the electromagnet are of considerable importance in suchconstructions. Furthermore, the material composition and the manner ofannealing are factors which affect the operational efficiency of amagnet insert in such devices.

The most important consideration, however, is the active airgap betweenthe pole surfaces of the magnet core and the abutment surface on theanchor or armature blade because this air gap is to be as small aspossible with spacings on the order of for instance less than I beinginvolved. This is difficult to obtain, but it is even more difficult tomake the pole surfaces at the free ends of the arms of the magnet corecompletely planar as well as having them be located in a common planewith one another, a requirement which should ideally be fulfilled inorder to assure that, when the electromagnetic device is assembled andit is in operational condition, the abutment surface of the anchor plateand the pole surfaces of the magnet member are as close as possible tobeing located in a plane common to them all, meaning that all threesurfaces should be located in a common plane. The more closely thisrequirement can be met, the more advantageous is the size of the contactarea between the contact surfaces and the surface of the anchor plate,and accordingly more pronounced will be the holding power of theelectromagnet.

The problem is that when the. pole surfaces on the two arms of theelectromagnetic core are being produced, both arms of the magnet memberor magnetic core tend to oscillate and therefore counteract the attemptto provide planar surfaces constituting the abutment surfaces. Theresult is that each individual pole or abutment surface in the endeffect is not planar but slightly curved and the planes of the polesurfaces on the respective arms are skew with reference to one another.Thus, even if the abutment surface on the anchor plate is absolutelyplanar, it is impossible to obtain a lano-parallel abutment between thissurface and the pole surfaces on the arms of the magnet core. This, inturn, means that a considerably smaller contact area between theabutment face of the anchor plate and the pole surfaces on the arms ofthe magnet core must be accepted and in practice this heretofore hasalways meant that specialists in the field have not decreased thediameter of the electromagnet below a certain minimum size, simply inorder to assure that the con tact area which it was possible to attainin view of the aforementioned difficulties would be sufficient toprovide the desired holding power of the electromagnet. Attempts tofurther treat the pole surfaces after annealing were made, but were notsuccessful to any significant extent in improvingthe planar condition ofthe pole surfaces, because it was again impossible to preventoscillation of the arms of the magnet core even if the yoke of the corewas fixedly held. For this reason the specialists in the field decidedthat the diameter of an electromagnetic core member with fixedlymountable yoke should not be decreased below 10 mm, and no such decreasehas heretofore become known.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to provide an improvement in the above-identified area of art.

More particularly, it is an object of the present invention to provide amethod of making an electromagnetic device wherein the area of contactbetween the pole surfaces and the abutment surface of the anchor platecan be significantly increased with concomitant possibility ofdecreasing the dimensions of the magnet core without however decreasingthe holding power of the electromagnet.

In pursuance of the above objects, and others which will become apparanthereafter, one feature of our invention resides in making anelectromagnetic device having an armature plate, a bifurcated magnetcore having a fixedly mounted yoke and a pair of arms cooperating withthe armature plate and each being provided with a pole surface facingthe same, and a winding applied onto the magnet core. In accordance withthe invention the inherent frequency of the fundamental oscillationi.e., the natural frequency of vibration of the magnet core prior toapplication of the winding is in excess of 25 kilohertz (kHz).

Thus, the invention is based on the finding that if the inherentfrequency of the fundamental oscillation caused mechanically as by aguiding or lapping wheel of the magnet core with fixedly mounted yokeand prior to application of the winding, is in excess of 25 kHz, thepole surfaces at the free ends of the arms of the magnet core can beproduced with such precision that they will be highly planar and alsowill both be located in one and the same plane rather than being skewwith reference to one another, thereby providing a significantlyincreased area of contact with the abutment surface of the armatureplate and permitting an extreme reduction in the dimensions of theelectromag netic device without adversely effecting the holding powerthereof.

In accordance with the preferred embodiment the inherent frequency ofthe fundamental oscillation of the non-wound magnet core is preferablyon the order of 30 kHz. The inherent frequency of one of the nonwoundarms by itself is higher than 30 kHz, preferably on the order of 34 kHz.The volume of one arm is less than mm, preferably smaller than 60 mm.The spacing between the two arms is smaller than the thickness of thearms and preferably the magnet core is extrusion molded fromsoft-magnetic material.

By resorting to the present invention the dimensions and the weight of adevice according to the invention can be reduced to a fraction of thevalues which heretofore were considered the lower limits by specialistsin the field.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammaticlongitudinal section through a thermo-electric ignition safety deviceutilizing an electromagnetic device made according to the presentinvention;

FIG. 2 is a fragmentary section through the device illustrated in FIG.1, on an enlarged scale;

FIG. 3 is a section taken on the line III III of FIG. 2 with the windinghaving been omitted; and

FIG. 4 is a section taken on the line IVIV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing indetail it is emphasized that the method of the present invention hasbeen illustrated on the basis of an ignition safety device which isthermo-electrically operated and which in itself is known. The devicecomprises a housing whose inner wall is provided with a valve seat 1 1for a valve member 12 of the safety valve. A gas inlet aperture 13 and agas outlet aperture 14 are provided on the housing 10.

The valve member 12 is connected with a valve stem or plunger 15 and ahelically convoluted spring 16 bears upon the valve member 12 urging thesame to valve-closing position, as is evident from FIGS. 1 and 2. Thefree end of the valve stem 15 extends into a mag netic device which isgenerally identified with reference numeral 20 and more clearlyillustrated in FIGS. 2-4.

As is particularly evident from FIG. 2, the device 20 comprises anarmature plate 21 which is connected with the valve stem 15 and anelectromagnet 22 which is of substantially U-shaped configuration. Thiselectromagnet, or bifurcated magnet core comprises a plate 221 whichconstitutes its yoke and which is of circular outline, and two arms 222and 223 extending from the plate 221 towards the armature plate 21 andhaving a substantially kidney-shaped cross-section (compare FIG. 3). Aperipherally projecting portion 224 is provided on the plate 221 in theregion of the base surface thereof and serves in known manner forconnecting the magnetic core 22 to a supporting plate 23 through itsafter the same is introduced into the housing 10, connected with mass ofthe housing 10. The other end of the winding is identified withreference numeral 241 and is passed through a bore 225 in the plate 221.

A contact member 25 is provided on the plate 23 in known manner, beinginsulated electrically with reference to the plate 23 and having a bore251 through which the end portion 241 of the winding 24 extends, the endportion 241 being connected with the member 25 in electricallyconductive manner, for instance by soldering or the like. Also connectedin known manner to the contact member 25 is the contact 261 of a thermalelement 26 shown in FIG. 1. The magnet core 22 and the anchor plate 21are in a manner which is also known per se by a protective'cap 27through and into which the valve stem 15 extends. That side of the cap27 which faces the closure member 12 of the valve serves at the sametime as an abutment for the spring 16.

The structural unit consisting of the magnet insert 20 including valvemember 12, anchor plate 21, magnet core 22, supporting plate 23 andcontact member 25, is inserted into the housing 10 of the device shownin FIG. 1 and is maintained in position by a screw cap 28 which at thesame time serves to secure the contact 261 of the thermal element 26.

A pushbutton 29 is shiftably inserted at that end of the housing 10which is opposite the magnetic insert 20; the pushbutton 29 is rigidlyconnected with a plunger 291 and is displaceable in the directiontowards the valve member 12 of the valve against the oppositely directedbiassing force of a return spring 30.

By displacing the pushbutton 29 with the plunger 291 oppositely theforce of the spring 30 the valve member 12 can be lifted off its valveseat 11 whereby at the same time the abutment surface of the anchorplate 21 is placed into abutment with the pole surfaces on the arms 222and 223 of the magnet core 22 when the gasoperated device which isprovided with the ignition safety device illustrated in FIG. 1, is to beput into operation.

The structural details which have heretofore been de scribed are knownfrom the art. In accordance with the present invention, however, thecontact area between the pole surfaces on the arms 222 and 223 of themagnet core 22 and the abutment surface of the anchor blade 21 issignificantly increased by assuring when carrying out the present methodthat the inherent frequency of the fundamental oscillation of the magnetcore 22 when the same does not carry the winding and when the yokeconstituted by the plate 221 is fixedly mounted is higher than 25 kHz(kilohertz). When this is the case in accordance with the presentinvention, it has been found that the pole surfaces at the free ends ofthe arms 222 and 223 of the magnet core 22 can be produced in such amanner that they will not only be highly planar but'also will be locatedin a common plane. This means that the slight curvature of each polesurface which heretofore was unavoidable to all intents and purposes, nolonger exists and further that the pole surfaces of the arms 222 and 223are no longer skew with reference to one another, or at least that thisfactor is reduced to an acceptable minimum. As a result, the contactarea between the pole surfaces of the arms 222 and 223 on the magnetcore 22 and the abutment surface on the anchor plate 21 is significantlyincreased.

' of the magnet core 22 be on the order of 30 kHz and that thefundamental frequency of one of the arms without the winding alone behigher than 30 kHz,

preferably on the order of 34 kHz. By resorting to the invention as justoutlined, the dimensions of the magnet core 22 may be significantlysmaller than it was heretofore thought possible by the experts while thedevice yet provides adequate holding power.

In the illustrated construction the volume of one of the arms 222 or 223of the magnet core 22 is less than 70 mm, preferably less than 60 mmFurthermore, the spacing between the two arms 222 and 223 is smallerthan the thickness of an individual arm.

Asa result, the diameter of the magnet core 22 is on the order of 7 mmand the total axial length of the magnet core 22 only insignificantlyexceeds this value. This is by contrast with a diameter of 10 mm whichheretofore was thought to be the lowermost practicable limit, andbecause of this reduction in the dimensions the weight of the magnetcore is correspondingly decreased and is only approximately one-quarterof the weight heretofore found in the smallest magnet core having adiameter of 10 mm.

It is evident that a reduction in the dimensions of the magnet core 22permits a corresponding reduction in the dimensions of the anchor plate21 and that the other parts of the magnetic insert 20 arecorrespondingly reduced in size so that in a device according to thepresent invention the outer diameter of the protective cap 27 needs onlybe approximately 10 mm whereas heretofore in the customary deviceshaving a magnet core with a diameter of 10 mm the outer diameter of theprotective cap was 14 mm.

The contact member 25 and the valve stem 15 may be unchanged as comparedto the known constructions, although it is of course possible toaccommodate the dimensions of the contact member 25 todifferently-dimensioned contact portions of a thermal element withoutaffecting the intent and scope of the present invention in any manner.

Of course, in making the magnet core it is necessary that the magnetcore be so produced that it have the desired inherent frequency of itsfundamental oscillation, and that thereupon the contact surfaces beproduced on the free ends of the arms 222 and 223 of the magnet core.Because the resulting contact surfaces are highly planar, and becausethey are located precisely in a common plane, the area of contactbetween the pole surfaces or contact surfaces on the arms 222 and 223and the abutment surface on the anchor plate 21 is significantly higherthan heretofore possible so that despite a decrease in the overall areaof the pole surfaces and of the abutment surface of the anchor plate 21the electromagnetic device still has the desired holding power.

While the present invention has been described herein with reference toits use in an ignition safety device on thermo-electric basisparticularly as used in gas-operated appliances and devices, it will beappreciated that the invention is not limited thereto and has a muchwider field of applicability.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described with reference tomaking of an electromagnetic device, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:

1. A method of providing on the arms of a bifurcated magnet core whoseyoke is to be fixedly mounted, re-

spective pole surfaces which are highly planar and strictly located in acommon plane so as to have a maximum area of contact with a planarabutment surface of an armature plate, said method comprising the stepsof forming a bifurcated magnet core blank having a yoke and a pair ofarms, from a magnet material having a natural frequency of vibrationwhich is in excess of 25 kHz when said yoke is fixedly mounted; formingon the free ends of said arms by a mechanical metal-working operationpole surfaces which are highly planar and strictly located in a commonplane, said natural frequency of vibration of said magnet material ofsaid bifurcated magnet core blank preventing vibration of saidbifurcated magnet core blank during said mechanical metal workingoperation so as not to interfere with said mechanical metal workingoperation and thus permit obtention of highly planar pole surfacesstrictly located in a common plane; and mounting said magnet core withthe thus obtained highly planar pole surfaces located in a common planein such a manner that said pole surfaces extend parallel to and facingsaid planar abutment surface of said armature plate.

2. A method as defined in claim 1, wherein said material has a naturalfrequency of vibration which is at least substantially equal to 30 kHzwhen said yoke is fixedly mounted.

3. A method as defined in claim 1, wherein each of said arms has anatural frequency of vibration which is in excess of 30 kHz when saidyoke is fixedly mounted.

4. A method as defined in claim 1, wherein each of said arms has anatural frequency of vibration which is substantially equal to 34 kHz.

5. A method as defined in claim 3, wherein the step of forming saidblank comprises providing the latter with said arms so dimensioned as tohave respective volumes smaller than mm".

6. A method as defined in claim 1, wherein the step of forming saidblank comprises press-molding said blank from said magnetic material.

7. A method as defined in claim 1, wherein the step of forming saidblank comprises making the blank with said arms spaced from one anotherby a distance which is smaller than the thickness of the respectivearms.

1. A method of providing on the arms of a bifurcated magnet core whoseyoke is to be fixedly mounted, respective pole surfaces which are highlyplanar and strictly located in a common plane so as to have a maximumarea of contact with a planar abutment surface of an armature plate,said method comprising the steps of forming a bifurcated magnet coreblank having a yoke and a pair of arms, from a magnet material having anatural frequency of vibration which is in excess of 25 kHz when saidyoke is fixedly mounted; forming on the free ends of said arms by amechanical metal-working operation pole surfaces which are highly planarand strictly located in a common plane, said natural frequency ofvibration of said magnet material of said bifurcated magnet core blankpreventing vibration of said bifurcated magnet core blank during saidmechanical metal working operation so as not to interfere with saidmechanical metal working operation and thus permit obtention of highlyplanar pole surfaces strictly located in a common plane; and mountingsaid magnet core with the thus obtained highly planar pole surfaceslocated in a common plane in such a manner that said pole surfacesextend parallel to and facing said planar abutment surface of saidarmature plate.
 2. A method as defined in claim 1, wherein said materialhas a natural frequency of vibration which is at least substantiallyequal to 30 kHz when said yoke is fixedly mounted.
 3. A method asdefined in claim 1, wherein each of said arms has a natural frequency ofvibration which is in excess of 30 kHz when said yoke is fixedlymounted.
 4. A method as defined in claim 1, wherein each of said armshas a natural frequency of vibration which is substantially equal to 34kHz.
 5. A method as defined in claim 3, wherein the step of forming saidblank comprises providing the latter with said arms so dimensioned as tohave respective volumes smaller than 70 mm3.
 6. A method as defined inclaim 1, wherein the step of forming said blank comprises press-moldingsaid blank from said magnetic material.
 7. A method as defined in claim1, wherein the step of forming said blank comprises making the blankwith said arms spaced from one another by a distance which is smallerthan the thickness of the respective arms.